1. Field of the Invention
The present invention relates to a resin film forming method, a resin film forming apparatus and an electronic circuit board manufacturing method, and more particularly, to technology for forming a prescribed resin film pattern on a substrate by ejecting droplets of resin liquid by means of an inkjet method.
2. Description of the Related Art
There are known methods for manufacturing electronic circuit boards or printed circuit boards, such as a subtractive method, a semi-additive method, an additive method, and the like, using photolithography as described below. Below, a brief description of these methods is given.
In the subtractive method, a copper clad laminate plate 902 composed of an insulating base material (insulating layer) 901 and copper foil conductor layers (conductive layers) 903 is prepared as shown in FIG. 17A. A hole 904 which is to form a through hole is formed in the copper clad laminate plate 902 as shown in FIG. 17B, and a conductor layer 907 is formed on the surface of the conductor layers 903 and the inside of the hole 904 by electroless plating or electrolytic plating, thereby creating a through hole 904 as shown in FIG. 17C. Then, resist layers 905 are formed by a dry film resist (DFR) or a liquid resist on the copper clad laminate plate 902 in which the through hole 904 has been formed, and the resist layers 905 are patterned as shown in FIG. 17D, by exposing and developing electronic circuit patterns in the resist layers 905 using a photo tool (not shown). Thereupon, the portions of the conductor layers 903 and 907 that have not been covered with the resist patterns (the resist layers 905) are removed by etching as shown in FIG. 17E, and finally the resist layers 905 are removed, thereby completing a printed circuit board 908 having prescribed circuit patterns as shown in FIG. 17F.
In the additive method, an insulating base material 911 is prepared as shown in FIG. 18A. A hole 914 which is to form a through hole is formed in the insulating base material 911 as shown in FIG. 18B. Then, resist layers 915 are formed by means of a dry film resist (DFR) or liquid resist on the insulating base material 911, and the resist layers 905 are patterned as shown in FIG. 18C, by exposing and developing electronic circuit patterns in the resist layer 905 using a photo tool (not shown). Thereupon, conductor layers 917 which are to be circuit patterns are formed by electroless plating on the portions of the insulating base material 911 that have not been covered with the resist layers 915, the conductor layers 917 are also formed inside the hole 914, thereby creating a through hole 914 as show in FIG. 18D, and finally the resist layers 915 are removed, thereby completing a printed circuit board 918 having prescribed circuit patterns as shown in FIG. 18E.
In the semi-additive method, an insulating base material 921 is prepared as shown in FIG. 19A. A hole 924 which is to form a through hole is formed in the insulating base material 921 as shown in FIG. 19B, and conductor layers 923 are formed on the surface of the insulating base material 921 and inside the clearance hole 924 by electro plating as shown in FIG. 19C. Then, resist layers 925 are formed by a dry film resist (DFR) or liquid resist, and the resist layers 925 are patterned as shown in FIG. 19D, by exposing and developing electronic circuit negative patterns in the resist layers 925, by using a photo tool (not shown). Thereupon, conductor layers 927 which are to be circuit patterns are formed by electrolytic plating as shown in FIG. 19E, taking the portions of the conductor layers 923 that have not been covered with the resist layers 925 as seed layers. Then, the resist layers 925 are removed as shown in FIG. 19F, and the portions of the conductor layers 923 that have not been plated with the conductor layers 927 are removed by etching, thereby completing a printed circuit board 928 having prescribed circuit patterns as shown in FIG. 19G.
In the above-described methods using the photolithography, the steps for creating the photo tool and performing exposure and development are required in order to obtain the desired resist pattern, and this is problematic in that it requires a large amount of time and involves significant cost. Furthermore, there is also a problem of processing the waste liquid from the development step.
Under these circumstances, a method has been proposed which prints a resist pattern directly by means of an inkjet system (see, for example, Japanese Patent Application Publication No. 56-66089). More specifically, droplets of a liquid resist material (resist ink) are ejected from an inkjet type ejection head (inkjet head) to directly print resist patterns onto a substrate, and by then carrying out etching using the resist patterns as a mask, it is possible to obtain a printed circuit board having desired wiring patterns (circuit patterns). By adopting this method, it is possible to eliminate the steps of creation of the photo tool, lamination with dry film resist (DFR), exposure and development.
Furthermore, methods for directly printing wiring patterns by means of an inkjet system have also been proposed (see, for example, Japanese Patent Application Publication Nos. 2004-000927 and 2004-351305). More specifically, a dispersion liquid containing conductive micro-particles dispersed in a dispersion medium is ejected in the form of droplets from an inkjet type of ejection head (an inkjet head), thereby printing desired wiring patterns directly onto a substrate, and it is possible to obtain a printed circuit board having prescribed wiring patterns. These methods are not limited to the manufacture of printed circuit boards, but may also be used appropriately for forming conductive film wiring patterns and films constituting color filters in various types of devices (for instance, a plasma type display device, a liquid crystal display device, an organic electroluminescence (EL) display device, and the like).
However, the above-described methods involve problems as follows.
The method in Japanese Patent Application Publication No. 56-66089 is for directly printing resist patterns by using the inkjet system, and more specifically, for directly printing resist (i.e., an ink including an acid-resistant material that forms a solid body upon drying) onto the surface of a copper foil, by means of the inkjet method. In this method, the steps of creation of the photo tool, lamination with dry film resist, exposure and development are eliminated, and therefore the related consumables, such as processing agents, and processing equipment, are not required. However, since the resist is printed by the inkjet method directly onto the surface of the copper foil as described above, then the droplets that have landed on the copper foil and not yet dried spread over the surface of the copper foil, and consequently, the droplets combine with each other giving rise to problems such as bulging (swelling of the wires), and jaggedness (undulations in the wires). In particular, since the viscosity is adjusted to 3 cP to 20 cP by means of a silicone varnish, then when the droplets having this low level of viscosity land on the surface of the copper foil, bulging is even more liable to occur. In other words, with this method, it is difficult to obtain desired resist patterns.
The method in Japanese Patent Application Publication No. 2004-000927 is for directly printing wiring patterns by using the inkjet system, and more specifically, by forming first patterns by first droplets L1 and then arranging second droplets L2 between the first patterns in order to unite the first patterns together. According to this method, it is possible to form film patterns having broad widths and good pattern edge shapes, and furthermore, since the film patterns have the broad widths, then beneficial effects are obtained in that electrical conductivity is good, and shorting, disconnections, and the like, are not liable to occur. In spite of these, even if there is no combination between the droplets L1 due to mutual contact between the droplets L1 in the first step of the droplet arrangement step, substantial wetting and spreading of the droplets L1 tend to occur, and in order to suppress these, it is necessary to process the surface of the substrate (providing a surface treatment) to make the surface capable of repelling the liquid material. In particular, if a self-assembling film forming method is used in the surface treatment step, then a long processing time is required since the film must be left for 2 to 3 days at room temperature and maintained at 100° C. for 3 hours, and therefore the manufacturing costs are high, and moreover, the film compound such as fluoroalkylsilane (FAS) is expensive. If a plasma irradiation method is used for the surface treatment step, then since the work must be carried out in a vacuum and requires use of a gas, and so on, then there are problems in that the number of processes and apparatuses required increases yet further. Furthermore, in the first step of the droplet arrangement step, removal of the diffusion medium is advanced by previously heating the substrate, which is desirable in order to stabilize the diameters of the droplets L1, and to standardize the film thickness while also achieving a large film thickness, but since the droplets L2 do not wet and spread over the surface when they are arranged, and furthermore, since the removal of the dispersion medium of the droplets L2 progresses simultaneously, then there is a risk that the droplets L2 do not fill in the gaps between the droplets L1 having been deposited.
The method in Japanese Patent Application Publication No. 2004-351305 is for directly printing wiring patterns by using the inkjet system, and more specifically, the method includes a first ejection step of depositing droplets at intervals within a region to be coated between liquid-repelling regions, and a second ejection step of depositing droplets within the region to be coated, at staggered deposition positions in comparison with the previous first deposition. By adopting this method, it is possible to achieve a film of large and uniform thickness, but in order to deposit the droplets onto the region to be coated, which is situated between the liquid-repelling regions formed by a liquid-repelling film, it is necessary to provide the repelling and non-repelling patterns on the substrate beforehand. In particular, if a self-assembling film forming method is used in the liquid-repelling treatment step, then problems similar to those of Japanese Patent Application Publication No. 2004-000927 arise. Furthermore, if an ultraviolet light irradiation method is used in the liquid-repelling treatment step, then a mask corresponding to the wiring patterns is required, and consequently, it is necessary to use the photolithographic method.